During completion of oil and gas wells, cement is often used to solidify a well casing within the newly drilled wellbore. To accomplish this, cement slurry is first pumped through the inner bore of the well casing and either out its distal end or through one or more ports defined in the well casing at predetermined locations. Cement slurry exits the well casing into the annulus formed between the well casing and the wellbore and is pumped back up toward the surface within the annulus. Once the cement hardens, it forms a seal between the well casing and the wellbore to protect oil producing zones and non-oil producing zones from contamination. In addition, the cement bonds the casing to the surrounding rock formation, thereby providing support and strength to the casing and also preventing blowouts and protecting the casing from corrosion.
Prior to cementing, the wellbore and the well casing are typically filled with drilling fluid or mud. A cementing plug is then pumped ahead of the cement slurry in order to prevent mixing of the drilling mud already disposed within the wellbore with the cement slurry. When the cementing plug reaches a collar or shoulder stop arranged within the casing at a predetermined location, the hydraulic pressure of the cement slurry ruptures the plug and enables the cement slurry to pass through the plug and then through either the distal end of the casing or the side ports and into the annulus. Subsequently, another cementing plug is pumped down the casing to prevent mixing of the cement slurry with additional drilling mud that will be pumped into the casing following the cement slurry. When the top cementing plug lands on the collar or stop shoulder, the pumping of the cement slurry ceases.
To perform the aforementioned cementing operations, a cement head and pumping unit are usually employed. The cement head is arranged at the surface of the wellbore in what is referred to as the “red” or high danger zone. The cementing plugs are held within the cement head until the cementing operation requires their deployment. Various valves associated with the cement head are required to be manipulated in order to perform the required tasks of the cement head. Such valves are typically manipulated manually, thereby requiring rig personnel to be in close proximity to the cement head (i.e., the red zone) and other wellbore equipment. In some cases, rig hands are required to be strapped and suspended in the air in order to operate the valves as the cement is pumped by the cement pumping unit. As can be appreciated, this presents a potential safety hazard.
Moreover, the cement pumping unit used to pump the cement is located remotely from the cement head, i.e., outside the red zone. In land wells, the pumping unit is typically about 150 yards away from the cement head, while in floating rigs the pumping unit is usually many floors away from the cement head. Thus, during cementing operations, the operator at the pumping unit control device must communicate with the rig hand at the cement head to instruct him when/how to operate the valves. Due to noise and other issues inherent in communication, the cement operation time is increased. Quite often, the operation must be suspended in order to allow communication between the pumping unit operator and cement head rig hand, further increasing the time and cost associated with cementing operations.